In recent years, applications of a three-dimensional (3D) shape measurement technology have been expanded to a field having a closer relationship with our lives such as ceramics industry, shoe industry, jewelry industry, and dental technology as well as engineering such as mechanical engineering and automotive engineering.
As an example of the related art for measuring the shape of the 3D object, a pattern projection method for projecting pattern light of a plurality of patterns on a subject and imaging the subject on which images of the pattern light are projected to perform a shape measurement using a principle of triangular measurement based on a deformation of the patterns has been known. Among these methods, a spatial encoding method for performing binary encoding on a space by projecting light of a stripe pattern in which bright parts and dark parts are alternately disposed at any width has been known in a field of a 3D measurement. Reviewing the 3D shape measurement process according to the spatial encoding method with reference to Korean Patent Laid-Open Publication No. 2001-0009721, first, a series of patterns is sequentially projected on an object to be measured and the patterns are repeatedly photographed by each camera to obtain (camera calibration) a relative position (external variable) and focal distances of cameras and a lens distortion coefficient (internal variable) based on a reference coordinate system and find out correspondence on which line of an image photographed by a second camera a specific line of an image photographed by a first camera corresponds to, prior to photographing an object to be measured by a CCD camera set Next, a computer controller uses pattern image information to obtain a 3D point data. For this purpose, one line having the same history among lines corresponding to the final pattern projected on each of the photographed images is taken as a sample and 3D coordinates of points forming the line are obtained.
Meanwhile, in addition to the spatial encoding method, as another method for measuring a shape of a 3D object by projecting a light pattern, a phase shift method has also been known. The phase shift method images lattice patterns on an object to be measured and then acquires phase values at each point of an image of the lattice patterns imaged on the object to be measured. Meanwhile, the detailed method for acquiring a phase from an image of lattice patterns is disclosed in ‘study on 3D image height information analysis using phase-shift interferometry (PSI)’ presented in collection of articles of academic conferences summer Jul. 14 to 17, 2009 by Korean Institute of Electrical Engineering.
The foregoing related arts correspond to the method for obtaining relatively higher measurement precision. However, in acquiring 3D information from 2D image information acquired by two cameras, the related arts may not acquire 3D point data for a specific point of an object to be measured when only one camera photographs the specific point of the object to be measured but the other camera does not photograph the specific point, due to a shape of the object to be measured or a position of the camera.